JP6162505B2 - Gradient coil and magnetic resonance imaging apparatus - Google Patents

Description

  Embodiments described herein relate generally to a gradient coil and a magnetic resonance imaging apparatus.

  Magnetic resonance imaging is based on magnetic resonance signal data generated by exciting the nuclear spin of a subject placed in a static magnetic field magnetically with an RF (Radio Frequency) pulse of the Larmor frequency. This is an imaging method for generating an image.

  Conventionally, a gradient magnetic field coil included in a magnetic resonance imaging apparatus is manufactured by laminating a plurality of coils and cooling tubes, impregnating (injecting) a resin (resin), and curing the resin. However, since the resin shrinks in the course of curing, there is a risk that cracks and peeling will occur at locations where the amount of impregnating resin is large.

JP 2010-088619 A

  The problem to be solved by the present invention is to provide a high-quality gradient coil and magnetic resonance imaging apparatus.

The gradient magnetic field coil according to the embodiment includes a saddle-shaped conductor portion formed in a substantially cylindrical shape with a conductive member. The conductor portion is different from the spiral of the first pattern to generate a magnetic field gradient, the central portion of the spiral, or were formed slits in the outer peripheral corner portion of the outside of the spiral, and the first pattern And a second pattern of stripes.

FIG. 1 is a functional block diagram showing the configuration of the MRI apparatus according to the first embodiment. FIG. 2 is a perspective view showing the structure of the gradient magnetic field coil according to the first embodiment. FIG. 3 is a view showing a pattern formed on a conductor portion according to the first embodiment. FIG. 4 is a view showing a second pattern formed on the conductor portion according to the first embodiment. FIG. 5 is a diagram illustrating an X coil according to the first embodiment. FIG. 6 is a view showing a Y coil according to the first embodiment. FIG. 7 is a diagram illustrating fixing of the X coil according to the second embodiment with a tape. FIG. 8 is a diagram illustrating fixing of the Y coil according to the second embodiment with a tape. FIG. 9 is a diagram illustrating a cross-section of the gradient magnetic field coil according to the second embodiment. FIG. 10 is a diagram illustrating fixing of an X coil according to a modification of the second embodiment with a tape. FIG. 11 is a diagram illustrating fixing of a Y coil according to a modification of the second embodiment with a tape.

  Hereinafter, a gradient magnetic field coil and a magnetic resonance imaging apparatus (hereinafter referred to as “MRI (Magnetic Resonance Imaging) apparatus” as appropriate) according to embodiments will be described with reference to the drawings. Note that the embodiments are not limited to the following embodiments. The contents described in each embodiment can be applied in the same manner to other embodiments in principle.

(First embodiment)
FIG. 1 is a functional block diagram showing the configuration of the MRI apparatus 100 according to the first embodiment. As shown in FIG. 1, the MRI apparatus 100 includes a static magnetic field magnet 101, a static magnetic field power supply 102, a gradient magnetic field coil 103, a gradient magnetic field power supply 104, an RF coil 105, a transmission unit 106, and a reception unit 107. A bed 108, a sequence control unit 120, and a computer 130. The MRI apparatus 100 does not include a subject P (for example, a human body). Moreover, the structure shown in FIG. 1 is only an example. Each unit may be appropriately integrated or separated.

  The static magnetic field magnet 101 is a magnet formed in a hollow cylindrical shape, and generates a static magnetic field in a space inside the cylinder. The static magnetic field magnet 101 is, for example, a superconducting magnet or the like, and is excited by receiving a current supplied from the static magnetic field power source 102. The static magnetic field power supply 102 supplies a current to the static magnetic field magnet 101. The static magnetic field magnet 101 may be a permanent magnet. In this case, the MRI apparatus 100 may not include the static magnetic field power source 102. In addition, the static magnetic field power source 102 may be provided separately from the MRI apparatus 100.

  The gradient magnetic field coil 103 is a coil disposed inside the static magnetic field magnet 101 and formed in a hollow cylindrical shape. The gradient coil 103 receives a current supplied from the gradient magnetic field power supply 104 and generates a gradient magnetic field. The gradient coil 103 will be described later in detail. The gradient magnetic field power supply 104 supplies a current to the gradient magnetic field coil 103.

  The RF coil 105 is disposed inside the gradient magnetic field coil 103 and receives a supply of RF pulses from the transmission unit 106 to generate a high-frequency magnetic field. Further, the RF coil 105 receives a magnetic resonance signal (hereinafter referred to as “MR (Magnetic Resonance) signal” as appropriate) generated from the subject P due to the influence of the high-frequency magnetic field, and outputs the received MR signal to the receiving unit 107.

  The above-described RF coil 105 is only an example. The RF coil 105 may be configured by combining one or more of a coil having only a transmission function, a coil having only a reception function, or a coil having a transmission / reception function. For example, the RF coil 105 is configured by a combination of a WB (Whole Body) coil having a transmission / reception function and a PA (Phased Array) coil having a reception function.

  The transmitter 106 supplies the RF coil 105 with an RF pulse corresponding to the Larmor frequency determined by the type of target atom and the magnetic field strength. The receiving unit 107 detects the MR signal output from the RF coil 105, and generates MR data based on the detected MR signal. Specifically, the receiving unit 107 generates MR data by digitally converting the MR signal output from the RF coil 105. The receiving unit 107 also sends the generated MR data to the sequence control unit 120. The receiving unit 107 may be provided on the gantry device side including the static magnetic field magnet 101, the gradient magnetic field coil 103, and the like.

  The bed 108 includes a top plate on which the subject P is placed. In FIG. 1, only this top plate is shown for convenience of explanation. Normally, the bed 108 is installed so that the central axis of the cylinder of the static magnetic field magnet 101 is parallel to the longitudinal direction. Further, the top plate is movable in the longitudinal direction and the vertical direction, and is inserted into the space inside the cylinder inside the RF coil 105 with the subject P placed thereon. The space inside the cylinder may be referred to as “bore” or the like.

  The sequence control unit 120 performs imaging of the subject P by driving the gradient magnetic field power source 104, the transmission unit 106, and the reception unit 107 based on the sequence information transmitted from the computer 130. Here, the sequence information is information defining a procedure for performing imaging. The sequence information includes the strength of the current supplied from the gradient magnetic field power supply 104 to the gradient magnetic field coil 103 and the timing of supplying the current, the strength of the RF pulse supplied from the transmitter 106 to the RF coil 105, the timing of applying the RF pulse, and reception. The timing at which the unit 107 detects the MR signal is defined.

  For example, the sequence control unit 120 is an integrated circuit such as an application specific integrated circuit (ASIC) or a field programmable gate array (FPGA), or an electronic circuit such as a central processing unit (CPU) or a micro processing unit (MPU).

  When the sequence controller 120 receives the MR data from the receiver 107 as a result of driving the gradient magnetic field power source 104, the transmitter 106, and the receiver 107 and imaging the subject P, the sequence controller 120 converts the received MR data to the computer 130. Forward to.

  The computer 130 performs overall control of the MRI apparatus 100. Further, the computer 130 generates MR images by performing reconstruction processing such as Fourier transform on the MR data transferred from the sequence control unit 120. For example, the computer 130 includes a control unit, a storage unit, an input unit, and a display unit. The control unit is an integrated circuit such as an ASIC or FPGA, or an electronic circuit such as a CPU or MPU. The storage unit is a RAM (Random Access Memory), a semiconductor memory device such as a flash memory, a hard disk, an optical disk, or the like. The input unit is a pointing device such as a mouse or a trackball, a selection device such as a mode switch, or an input device such as a keyboard. The display unit is a display device such as a liquid crystal display.

  FIG. 2 is a perspective view showing the structure of the gradient coil 103 according to the first embodiment. Here, in the first embodiment, the gradient magnetic field coil 103 is an ASGC (Actively Shielded Gradient Coil), and a main coil 103a that generates a gradient magnetic field, and a shield coil 103b that generates a shield magnetic field that cancels the leakage magnetic field. And have. As shown in FIG. 2, in the gradient magnetic field coil 103, a main coil 103a, a cooling layer 103d in which a cooling pipe is piped, and a shim layer in which a shim tray is arranged in order from the inner side where the distance from the space inside the cylinder is short. 103c, a cooling layer 103e to which a cooling pipe is piped, and a shield coil 103b are laminated.

  A plurality of (for example, 24) shim tray insertion guides 103f are formed on the shim layer 103c. As shown in FIG. 2, the shim tray insertion guide 103f is typically a hole that penetrates the entire length of the gradient magnetic field coil 103 in the major axis direction, and is formed at equal intervals in the circumferential direction. Each of the shim trays (not shown) inserted into the shim tray insertion guide 103f has, for example, a plurality of (for example, 15) pockets in the longitudinal direction, and a predetermined pocket is used to correct the static magnetic field inhomogeneity. A predetermined number of iron shims are stored.

  The cooling layer 103d and the cooling layer 103e are typically provided with a cooling pipe spirally along a cylindrical shape (not shown in FIG. 2). Although not shown in FIG. 1, the MRI apparatus 100 according to the first embodiment further includes a cooling device having a heat exchanger and a circulation pump, and this cooling device circulates a coolant such as water through the cooling pipe. As a result, the gradient coil 103 is cooled.

  By the way, the main coil 103a is formed by stacking three coils corresponding to the X, Y, and Z axes orthogonal to each other, that is, an X coil, a Y coil, and a Z coil. The X coil is a coil processed into a saddle coil type, and generates a gradient magnetic field along the X axis, that is, the horizontal axis of the cylinder of the gradient coil 103. The Y coil is a coil processed into a saddle coil type like the X coil, but generates a gradient magnetic field along the Y axis, that is, the vertical axis of the cylinder of the gradient magnetic field coil 103. The Z coil is a coil processed into a spiral shape, and generates a gradient magnetic field along the Z axis, that is, the long axis of the cylinder of the gradient magnetic field coil 103. Each of these X coil, Y coil, and Z coil is individually supplied with a current from the gradient magnetic field power supply 104 and generates a gradient magnetic field whose magnetic field strength varies along each of the X, Y, and Z axes. . Similarly, the shield coil 103b is formed by laminating three coils corresponding to the X, Y, and Z axes orthogonal to each other, that is, an X coil, a Y coil, and a Z coil. Moreover, the stacking order of the coils can be changed as appropriate.

  Below, among the coils described above, the X coil and Y coil of the main coil 103a and the X coil and Y coil of the shield coil 103b will be described. Hereinafter, the main coil 103a and the shield coil 103b may be simply referred to as an X coil and a Y coil without being distinguished from each other.

  In the first embodiment, each of the X coil and the Y coil is formed by winding four conductive plates around the bobbin of the gradient coil 103. Hereinafter, the X coil and the Y coil formed by combining the conductive plates as described above may be referred to as “conductor portion 10X”, “conductor portion 10Y”, or “conductor portion” without distinction. is there.

  FIG. 3 is a view showing one conductive plate among the conductor portions according to the first embodiment, and is a view showing a pattern formed on the conductive plate. In the first embodiment, the X coil and the Y coil are formed by processing a predetermined pattern (for example, cutting, edging, etc.) on a conductive plate (for example, a copper plate, an aluminum plate, etc.). ing. Specifically, as shown in FIG. 3, a spiral first pattern and a second pattern different from the spiral first pattern are formed on the conductive plate. The second pattern is a fringe pattern substantially parallel to the cylindrical axial direction of the gradient coil 103.

  The spiral first pattern is formed over almost the entire surface of one conductive plate. This first pattern functions as a saddle coil. On the other hand, as shown in FIG. 3, the second stripe pattern is formed at the inner central portion of the spiral first pattern or at the outer peripheral corner of the spiral first pattern. In other words, the second pattern of stripes is formed in an empty space in the conductive plate where the first pattern is not formed.

  FIG. 4 is a diagram illustrating a second pattern formed on the conductor portion according to the first embodiment. FIG. 4 shows a perspective view of the second pattern formed at the outer peripheral corner of the spiral first pattern among the second patterns shown in FIG. 3. In FIG. 4, the surface of the conductive plate is indicated by dots, and the cross section is indicated by oblique lines.

  As shown in FIG. 4, in the first embodiment, the second pattern is a slit that penetrates to the back of the conductive plate and is engraved in a thin line shape with respect to the plate. Although not shown, the second pattern formed in the central portion inside the spiral first pattern of the second pattern shown in FIG. 3 also penetrates to the back of the conductive plate. On the other hand, it is a slit carved into a thin line.

  As described above, in the first embodiment, the conductive plate is left without being cut off even in the conductive plate where the first pattern is not formed. The amount of injected resin can be reduced, and cracks and peeling can be suppressed. As a result, insulation deterioration can be suppressed.

  Further, if the conductive plate is simply left, eddy current may be generated in the portion. In the first embodiment, in the portion where the conductive plate is left, the cylindrical axial direction, That is, since the slit in the direction substantially parallel to the static magnetic field direction is formed, the generation of eddy current can be prevented. In addition, when a slit in a direction substantially parallel to the static magnetic field direction is formed, Lorentz force does not act on the region of the second pattern, so the region where the second pattern is formed (for example, the outer corner) There is no risk of moving during imaging. In addition, when a slit in a direction substantially parallel to the static magnetic field direction is formed, the region in which the second pattern is formed does not generate a magnetic field component (Bz component) used for imaging, and thus has an effect on imaging. Can also be eliminated.

  Furthermore, in the first embodiment, the first pattern and the second pattern are formed by mechanical processing on the conductive plate. For this reason, for example, in order to suppress cracks and peeling, it is possible to reduce the number of man-hours for manufacturing the gradient magnetic field coil 103 as compared with the method of manually filling the empty space. In addition, the quality can be stabilized as compared with the manual filling method.

  The embodiment is not limited to the first pattern and the second pattern shown in FIGS. 3 and 4. The spiral shape of the first pattern, the number of turns, the pattern width, the width between patterns, and the like can be arbitrarily changed. Moreover, in FIG. 3, although the 2nd pattern demonstrated the example currently formed in the center part inside the spiral 1st pattern, or the outer periphery corner | angular part outside the spiral 1st pattern, embodiment is described. It is not limited to this. For example, the second pattern may be appropriately formed at a location where the pattern width is wide, a location where the width between the patterns is wide, or the like in the spiral first pattern itself. In other words, the region where the second pattern is formed is not limited to the example of FIG. 3, and may be appropriately provided at a location desired from the viewpoint of suppressing cracks and peeling.

  FIG. 5 is a diagram illustrating the X coil according to the first embodiment, and FIG. 6 is a diagram illustrating the Y coil according to the first embodiment. As described above, in the first embodiment, each of the X coil and the Y coil is formed by winding four conductive plates around the bobbin of the gradient magnetic field coil 103. Specifically, as shown in FIGS. 5 and 6, two conductive plates are arranged side by side in the axial direction of the bobbin that is the core of the gradient magnetic field coil 103, and a set of the two conductive plates is arranged. Are formed by winding two sets in the circumferential direction around the bobbin. As can be seen by comparing FIG. 5 and FIG. 6, the Y coil has the same configuration as that obtained by rotating the X coil by 90 ° about the axis of the cylinder.

  As described above, the gradient coil 103 is formed by laminating a plurality of layers. In FIGS. 5 and 6, layers other than the X coil and layers other than the Y coil are omitted. 5 and 6 show an example in which four conductive plates are spread without gaps, but the embodiment is not limited to this, and the arrangement relationship of the four plates is appropriately set. Can be changed.

  As described above, according to the first embodiment, since the member is left even in the portion where the spiral pattern is not formed in the saddle coil type coil, the amount of impregnating resin can be reduced, and cracks and peeling Can be suppressed. In addition, according to the first embodiment, the remaining conductive member is formed with slits in a direction substantially parallel to the static magnetic field direction, so that eddy currents, Lorentz forces, and magnetic field components that affect imaging are generated. Can be prevented. Furthermore, according to the first embodiment, since it is a technique by mechanical processing on the conductive plate, it is possible to contribute to the reduction in the number of manufacturing steps of the gradient magnetic field coil 103 and the stability of the quality.

(Second Embodiment)
In the second embodiment, a method of further fixing the X coil and the Y coil wound around the bobbin of the gradient magnetic field coil 103 with a tape or the like will be described.

  FIG. 7 is a diagram illustrating the fixing of the X coil according to the second embodiment with a tape, and FIG. 8 is a diagram illustrating the fixing of the Y coil according to the second embodiment with a tape. As shown in FIGS. 7 and 8, in the second embodiment, a tape is wound around and fixed to the X coil and the Y coil. In FIGS. 7 and 8, the X coil and Y coil patterns hidden under the tape when the tape is wound are indicated by broken lines for convenience of explanation. In the case where the tape is a permeable material, the X coil and Y coil patterns can be visually recognized.

  Here, as shown in FIGS. 7 and 8, in the second embodiment, the tape is spirally wound along the circumferential direction of the bobbin. The degree of overlap between the tapes when spirally wound can be adjusted as appropriate. Moreover, as shown in FIG.7 and FIG.8, a tape is wound separately in the 1st fixed range and the 2nd fixed range. That is, the tape wound around the first fixed range and the tape wound around the second fixed range are not a series of tapes but separate tapes. In other words, the tape is wound in units of regions divided into two or more in the axial direction of the bobbin, and in each of the conductive plates in the second embodiment.

  In consideration of Lorentz force acting on each coil during imaging, it is desirable to use a tape having a certain tensile strength and elastic modulus. For example, a tape made of poly-paraphenylene benzobisoxazole (known as “Zylon”) can be used. Further, for example, a tape made of a material of poly-paraphenylene terephthalamide (known by the name “KEVLAR (registered trademark)”) can be used. The material of the tape is not limited to the material described above.

  FIG. 9 is a diagram showing a cross section of the gradient coil 103 in the second embodiment. In addition, it is a partial cross section of the gradient magnetic field coil 103, for example, shows a cross section on the shield coil 103b side. For example, as shown in FIG. 9, when the cooling pipe, the Z coil, the Y coil, and the X coil are sequentially stacked while sandwiching the insulating plate as appropriate from the bottom, for example, on the outside of the Y coil and the X coil, Tape is wound. Note that the winding of the tape is not limited to the example of FIG. For example, the stacking order of the coils can be changed as appropriate. The relationship between the coil pattern width and the tape width can also be changed as appropriate. Further, the degree of tape overlap can be changed as appropriate. Further, in FIG. 9, the example in which the tape is wound around both the Y coil and the X coil has been described, but the embodiment is not limited thereto. For example, the tape may be wound around only one of them. Further, it may be wound around the Z coil.

  As described above, according to the second embodiment, since the tape is spirally wound around the X coil and the Y coil in the circumferential direction, each coil moves due to the influence of the Lorentz force generated during imaging. The situation can be appropriately suppressed. Further, according to the second embodiment, as described in the first embodiment, since the member is left also in the portion where the spiral pattern is not formed, the clamping force by the tape is also applied to the lower layer. Can be properly transmitted and properly fixed. For example, when fixing with a tape, it is possible to avoid a situation in which the insulating plate is damaged by the surface pressure of the tape. In particular, although the Lorentz force generated at both ends of the cylinder of the gradient coil 103 tends to increase, members are left in the second pattern at both ends, and the tape is wound around the second pattern. Therefore, the tape is properly tightened.

(Modification of the second embodiment)
FIG. 10 is a diagram illustrating fixing of an X coil according to a modification of the second embodiment with a tape, and FIG. 11 is a diagram illustrating fixing of a Y coil according to a modification of the second embodiment with a tape. is there. Although FIG.7 and FIG.8 showed the example where a tape is wound over the whole electroconductive board, embodiment is not restricted to this. For example, as shown in FIGS. 10 and 11, the tape may be wound only on both ends of the cylinder of the gradient coil 103. The winding width and the like can be changed as appropriate.

(Other embodiments)
The embodiment is not limited to the above-described embodiment.

(Second pattern)
In the embodiment described above, the second pattern is a fringe pattern substantially parallel to the cylindrical axial direction of the gradient coil 103, but the embodiment is not limited thereto. The second pattern may be another pattern as long as the amount of the impregnating resin is appropriately reduced and generation of eddy current is appropriately suppressed. For example, a pattern including a curve may be used instead of a “stripe” formed by a straight line. Further, the second pattern is not limited to one type, and may be a combination of a plurality of types.

  Moreover, in embodiment mentioned above, although what was formed by processing an electroconductive board as an X coil or a Y coil was assumed, embodiment is not restricted to this. The first pattern of the X coil and the Y coil may be formed by winding a conductive wire in a spiral shape. In this case, the second pattern is formed so as to fill the empty space of the first pattern using, for example, a conductive or non-conductive wire.

  In the embodiment described above, an ASGC coil is assumed as the gradient coil 103, but the embodiment is not limited to this. In the above-described embodiment, an example in which the X coil and the Y coil, which are saddle coils, are formed using four conductive plates has been described. However, the embodiment is not limited thereto. The number of conductive plates, the arrangement method, and the like can be changed as appropriate.

  According to at least one embodiment described above, a high-quality gradient coil and a magnetic resonance imaging apparatus can be provided.

  Although several embodiments of the present invention have been described, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the spirit of the invention. These embodiments and their modifications are included in the scope and gist of the invention, and are also included in the invention described in the claims and the equivalents thereof.

DESCRIPTION OF SYMBOLS 100 MRI apparatus 103 Gradient magnetic field coil 103a Main coil 103b Shield coil 10X Conductor part (X coil)
10Y Conductor (Y coil)

Claims (9)

A saddle type conductor portion formed in a substantially cylindrical shape with a conductive member,
The conductor portion is different from the spiral of the first pattern to generate a magnetic field gradient, the central portion of the spiral, or were formed slits in the outer peripheral corner portion of the outside of the spiral, and the first pattern A gradient coil having a second pattern of stripes. The gradient magnetic field coil according to claim 1, wherein the second pattern is formed by inserting a slit substantially parallel to the axial direction of the substantially cylindrical shape. The conductor portion, the first pattern and the second pattern is a plate of electrically conductive, which is processed, the gradient coil according to claim 1 or 2. The conductor portions are provided as an X coil and a Y coil, respectively.
Each conductor portion is formed in a substantially cylindrical shape are laminated, the gaps between the conductor portions are laminated, the resin is impregnated, the gradient coil according to any one of claims 1 to 3. The gradient magnetic field coil according to any one of claims 1 to 4 , wherein a tape is wound around the conductor portion in a spiral shape along a circumferential direction. The gradient magnetic field coil according to claim 5 , wherein the tape is wound around the conductor portion in a unit of a region divided into two or more in the axial direction of the substantially cylindrical shape. The conductor portion is formed by arranging a plurality of conductive plates in the axial direction of the substantially cylindrical shape,
The gradient magnetic field coil according to claim 5 , wherein the tape is wound around each conductive plate. The gradient magnetic field coil according to claim 5 , wherein the tape is wound around the second pattern in the conductor portion. A static magnetic field magnet that generates a static magnetic field;
A gradient magnetic field coil for generating a gradient magnetic field,
The gradient coil is
A saddle type conductor portion formed in a substantially cylindrical shape with a conductive member,
The conductor portion is different from the spiral of the first pattern to generate a magnetic field gradient, the central portion of the spiral, or were formed slits in the outer peripheral corner portion of the outside of the spiral, and the first pattern A magnetic resonance imaging apparatus having a second pattern of stripes.

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